A method of randomizing digital bits or pixels to obscure low frequency patterns while preserving the data by XORing a predetermined high frequency bit pattern to the data, thereby breaking up long strings of bits of the same state.
The printing of digital bits as pixels results in patterns of 1""s and 0""s, usually to form an image. However, there are times when the information in the data is in the numerical content of the data, and the xe2x80x9cimagexe2x80x9d is preferably obscured.
An example is a section of glyphs containing numerical data. A glyph is a diagonal line that slopes at one angle to indicate one state of a bit, and at a different angle to indicate the other state. Here, the information is in numerical or word form, and there is no image. The glyphs are small, and are designed to appear as a gray background. The problem is that frequent long strings of 0""s or 1""s in the data will show up as patterns that visibly stand out in the glyph area. It would be advantageous to be able to break up these low frequency patterns that visibly stand out without destroying any data.
Numerous patents have issued on the generation and use of glyphs, such as U.S. Pat. No. 5,245,165, Self-Clocking Glyph Code for Encoding Dual Bit Digital Values Robustly; U.S. Pat. No. 5,449,895, Explicit Synchronization for Self-Clocking Glyph Codes; and U.S. Pat. No. 5,521,372, Framing Codes for Robust Synchronization and Addressing of Self-Clocking Glyph Codes, which are incorporated by reference herein.
This invention removes most low frequency patterns in the data by combining any kind of high frequency pattern with the data. An example of a high frequency pattern would be alternate 1""s and 0""s , and an example of a combining function could be an XOR function. The result would be that long strings of one state would be changed into high frequency patterns, and the resultant pattern could be printed to appear as a uniform gray area.
After printing, the data could be retrieved by inverting the original function, XOR in the example. Thus, the low frequency patterns can be obscured without the loss of data.